The long-range objectives of this project are to better understand the complex neuronal alterations that occur as a result of alcohol exposure and contribute to high alcohol drinking and relapse behaviors in genetically vulnerable subjects. Compelling evidence implicates the ventral tegmental area (VTA) and nucleus accumbens (ACB) in mediating the reinforcing effects of ethanol (EtOH) and alcohol drinking. The overall hypothesis to be tested is that the mesolimbic system of genetically vulnerable subjects is sensitive to EtOH and undergoes molecular neurobiological changes that contribute to high alcohol drinking and relapse behavior. The overall hypothesis will be tested in the selectively bred alcohol-preferring (P) and high-alcoholdrinking (HAD) lines of rats, using a micro-punch technique to isolate the VTA and the ACB-shell (sh). Stateof- the-art microarray procedures will be used to determine (a) acute EtOH-responsive genes in the VTA and ACB-sh, and (b) changes in gene expression that result from chronic alcohol self-administration and persist in the absence of alcohol. Two of the aims will determine genes that are differentially responsive to EtOH in lines of rats that respond differently to EtOH and have different alcohol drinking characteristics, i.e., P and HAD rats and their low-alcohol-consuming counterparts, alcohol-non-preferring (NP) and low-alcoholdrinking (LAD) rats. Two other aims will use operant techniques to determine the effects of EtOH selfadministration by P and HAD rats on gene expression in the VTA and ACB-sh, and whether some of the changes in gene expression produced by chronic EtOH self-administration persist in the absence of EtOH. The results of these latter two aims will identify genes that have altered expression due to chronic EtOH selfadministration and may contribute to relapse. Overall, the findings from this project will provide valuable information on EtOH-induced molecular neurobiological changes that occur within limbic regions of vulnerable individuals and may contribute to high alcohol drinking behavior and alcohol relapse. Such information would be important for determining potentially therapeutic pharmacological treatments for reducing alcohol drinking and relapse.